The present invention generally relates to the construction of electric motors. More specifically, the present invention relates to an electric motor having a capacitor assembly for the creation of an electrical phase shift to generate a rotating magnetic field in a single-phase AC motor.
As is known, electric motors include a stator and an armature (or rotor) with windings thereon. The motor is designed so that electric current through the stator and armature windings will generate opposed magnetic fields. Rotation of the motor shaft occurs as these magnetic fields attempt to align.
In an AC motor, it has been common practice in the industry to use a capacitor in the motor input circuit to create an electrical phase shift to generate a rotating magnetic field. Typical capacitor assemblies currently used in electric motors are either contained within the motor sleeve itself or are attached externally to the motor sleeve through the use of attachment hardware.
Referring now to FIG. 1, thereshown is a prior art configuration for the external mounting of a capacitor 10 to the motor sleeve 12 of an AC motor. As can be seen in FIG. 1, the motor sleeve 12 includes a pair of mounting studs 14 that extend from the generally cylindrical outer wall of the motor sleeve. During the construction of the motor incorporating the motor sleeve 12, the mounting studs 14 must be installed as a separate mounting step. The mounting studs 14 are spaced to allow the capacitor 10 to be positioned therebetween such that a metallic mounting strap 16 can be fitted over the capacitor 10 and secured to the mounting studs 14 by a pair of threaded nuts 18. Specifically, the metallic mounting strap 16 includes a pair of mounting holes 20 that receive the studs 14 and are secured by the pair of nuts 18.
The external capacitor 10 includes a pair of attached terminals (not shown, hidden under rubber boot 21). The two capacitor leads with attached mating terminals (not shown) extend out through the lead exit of the motor sleeve from the electric motor (stator assembly) in the interior of the motor sleeve 12 where they connect to the input power terminals for the AC motor. The rubber boot 21 is strung over the leads that extend out from the electric motor (stator assembly) through the lead exit of the motor sleeve. Once the external capacitor 10 is attached by the mounting bracket 16 and the capacitor lead terminals are connected to the capacitor terminals, the rubber boot 21 is installed over the entire arrangement to electrically insulate the capacitor, capacitor lead wires and their respective terminals. Again, the installation of the rubber boot 21 requires another step in the motor assembly process.
Although the attachment arrangement illustrated in FIG. 1 is an effective way to attach the external capacitor 10, additional parts and labor are required to fasten the capacitor 10 to the motor sleeve 12 and install the rubber boot 21 over the entire assembly. These additional parts and labor increase the overall costs and complexity of the motor.
Therefore, a need exists for an improved method and configuration for attaching an external capacitor to the outer motor sleeve of an electric motor. Further, a need exists for an external capacitor and respective leads that are adequately shielded and protected from external elements after the capacitor has been attached to the exterior of the motor sleeve.
The present invention is a case retained external capacitor that can be installed along the outer housing of an electric motor. The case retained capacitor of the present invention allows the capacitor to be installed during construction of an electric motor without requiring additional tooling, parts or manufacturing steps.
The case retained external capacitor includes a capacitor case that defines an open interior sized to receive a capacitor having attached lead wires. The lead wires of the capacitor are designed to be connected to the electric motor positioned within an external motor sleeve that surrounds the electric motor. The capacitor case is constructed having an inner wall that is positioned adjacent to the outer surface of the motor sleeve. The inner wall of the capacitor case includes a mounting clip that is formed to be received within an attachment slot stamped into the metallic motor sleeve. The attachment slot is formed such that it extends axially from a first end of the motor sleeve.
The mounting clip is formed integrally with the inner wall of the capacitor case and includes a pair of spaced receiving slots. The receiving slots of the mounting clip have a width to receive the thickness of the outer wall of the motor sleeve such that the capacitor case can be slid into the attachment slot. The mounting clip of the capacitor case includes a central notch that allows the leads of the contained capacitor to pass through the central notch and into the electric motor for connection across the power terminals of the electric motor.
Once the capacitor leads have been connected to the electric motor, an end plate is attached to the first end of the motor sleeve. The outer circumference of the end plate closes the attachment slot and prevents the mounting clip from being removed from the motor sleeve.
In one embodiment of the invention, the pair of sidewalls that define the capacitor case extend past the inner wall of the capacitor case and define a pair of standoff legs. The standoff legs each include a molded peg that is in contact with the outer surface of the motor sleeve such that the pegs and standoff legs create an air gap between the inner wall of the capacitor case and the outer surface of the motor sleeve.
In another embodiment of the invention, the capacitor case includes a standoff extension that extends from the inner wall of the capacitor case and provides additional spacing between the inner wall of the capacitor case and the outer surface of the motor sleeve. The standoff extension is formed along only a portion of the inner wall of the capacitor case.
In yet a further embodiment of the invention, the mounting clip formed along the capacitor case includes a pair of receiving slots that each include an angled wedge surface. Each wedge surface terminates at a top surface spaced slightly beneath the top end of the mounting clip. In this embodiment of the invention, the attachment slot formed in the motor sleeve is formed by a pair of angled sidewalls each of which include a retaining tab. The retaining tabs engage the top surfaces on the wedges to securely hold the mounting clip in place within the attachment slot.
During construction of the case retained external capacitor of the present invention, an initial supply of epoxy is poured into the open interior of the capacitor case. The capacitor material is then positioned within the capacitor case and the initial epoxy and the leads for the capacitor are positioned within the central notch formed in the mounting clip. Once the capacitor and leads are in place, a further supply of epoxy is poured into the open interior of the capacitor case such that the capacitor is waterproofed by the supply of epoxy.
Once the case retained external capacitor has been formed, the mounting clip is slid into the attachment slot formed in the motor sleeve and the capacitor leads connected to the electric motor. After the capacitor case has been properly positioned along the motor sleeve, the motor end plate is attached to prevent the capacitor case from becoming disengaged from the motor sleeve.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.